As a conventional displacement type fluid machine, a reciprocating fluid machine for moving a working fluid by repeating a reciprocation of a piston in a cylindrical cylinder, a rotary (rolling piston type) fluid machine for moving a working fluid by eccentrically rotating a cylindrical piston in a cylindrical cylinder, a scroll fluid machine for moving a working fluid by engaging a pair of fixed scroll and orbiting scroll, which have spiral wraps and stand up on end plates, with each other and by gyrating the orbiting scroll, are well known.
Since the reciprocating fluid machine is simply constructed, it is possible to prepare the machine easily and to be inexpensive. On the other hand, since the process from suction completion to discharge completion is short of the shaft angle of 180.degree. so that a flow velocity of the process for the discharge gets faster, there is a problem that the pressure loss is increased so that the performance is reduced. Further, since it is necessary to reciprocate the piston, so that a rotary shaft system can not be completely balanced, there is another problem that a vibration and a noise are larger.
Also, in case of the rotary fluid machine, since the process from suction completion to discharge completion has the shaft angle of 360.degree., there is less problem that the pressure loss during the discharge process is increased compared to the reciprocating fluid machine. However, since the working fluid is discharged once per one rotation of the shaft, the variation of a gas compression torque is relatively higher, accordingly, there is the same problem of the vibration and noise as the reciprocating fluid machine.
Further, in case of the scroll fluid machine, since the process from suction completion to discharge completion has the long shaft angle of 360.degree. or more (the scroll fluid machine practically used as an air conditioner has usually 900.degree.), so that the pressure loss during the process of discharge is low, a plurality of working chambers are formed generally, so that there is an advantage that the variation of the gas compression torque is low and the vibration and noise are less. When the wraps are engaged, it is necessary to manage the clearance between the spiral wraps and the clearance between the end plate and a wrap tip. Thus, the fluid machine must be worked with high accuracy, so that there is further problem that the expense of working is expensive. Further, since the process from suction completion to discharge completion has the long shaft angle of 360.degree. or more, it takes a long time for the compression process, so that there is further problem that the internal leakage is increased.
By the way, known is a displacement type fluid machine in which a displacer for moving a working fluid is not rotated relative to a cylinder in which the working fluid is suctioned, but is gyrated with an almost constant radius, that is, is gyrated to transmit the working fluid. This kind of displacement type fluid machines have been proposed in Japanese Patent Unexamined Publication No. 55-23353 (Document 1), U.S. Pat. No. 2,112,890 (Document 2), Japanese Patent Unexamined Publication No. 5-202869 (Document 3) and Japanese Patent Unexamined Publication No. 6-280758 (Document 4). Such a displacement type fluid machine as proposed therein comprises a petal-shaped piston having a plurality of members (vanes) radially extending from the center and a cylinder having a hollow portion of almost the same shape as the piston, wherein the piston is gyrated in the cylinder so as to move the working fluid.